Loudspeakers



Jan. 26, 1960 MANLEY 2,922,851

LOUDSPEAKERS Filed May 10, 1957 I8 fy. 1 4

6 llllll IO l6 l8 H I2 l5 9 'llllllllllll l4 8 l6 l8 '2 3 '5 llllll INVENTOR. FRED A. MANLEY ATTORNEY Uie States Patent 2,922,851 LOUDSPEAKERS Fred A. Manley, Rochester, N.Y., assignor to General Dynamics Corporation, Rochester, N.Y., a corporation of Delaware Application May 10, 1957, Serial No. 658,449

6 Claims. (Cl. 179 115.5)

The present invention relates to loudspeaker devices and, more particularly, to loudspeaker devices having a relatively flat response characteristic over the audio frequency spectrum.

A specific loudspeaker device will generally provide a relatively flat reproduction only over a portion of the audio frequency spectrum. Through proper design, however, it is possible to produce loudspeaker devices which afford a relatively flat reproduction at the low, intermediate, or high audio frequencies.

A variety of prior art schemes have been advanced for the purpose of providing a relatively fiat response throughout the entire audio frequency range. Among these schemes is the use of two or more separate loudspeaker units, arranged in the same plane or coaxially, each designed for a relatively flat response over respective portions of the audio frequency range, and the associated carefully designed cross-over or filter networks which are necessary to impress upon each loudspeaker device electric signals in that respective portion of the audio frequency spectrum which it is specifically designed to faithfully reproduce. Another arrangement which has been employed is the use of two or more radiating surfaces coaxially arranged in respect to a common magnetic circuit.

Although these systems generally afford a satisfactory reproduction, they all involve considerable expense in that they require two or more units or a massive magnetic circuit.

It is an object of this invention to provide an improved loudspeaker device which will obviate the disadvantage of the prior art.

It is another object of this invention to provide an improved loudspeaker device which will produce a relatively flat response over the audio frequency spectrum.

In accordance with this invention, a high frequency radiating surface is superimposed upon a low frequency radiating surface, thereby providing a radiating medium which produces a relatively fiat frequency response characteristic.

For a better understanding of the present invention, together with further objects, advantages, and features thereof, reference is made to the following description and accompanying drawing, in which:

Figure 1 is a front view of loudspeaker unit, incorporating the features of this invention, which indicates the respective detailed section views shown in Figures 2 and 3.

Figure 2 is a cross-section view, 2-2 of Figure 1, of a permanent magnet loudspeaker incorporating the features of this invention.

Figure 3 is cross-section view of the portion of Figure 1 indicated at 3-3.

The present description is in reference to an application of this invention to an electro-mechanical permanent magnet type loudspeaker for purposes of illustration only and in no way intends or infers that the principles of this invention be limited or restricted thereto. It is to be understood that this invention may be used in conjunction with an electrodynamic-type loudspeaker or any other 2 type electro-acoustical transducer device in which a relatively fiat frequency response is desired.

In Figure 2 is illustrated a permanent magnet type electro-mechanical loudspeaker device consisting of a pot assembly 1, a permanent magnet 2, a pole piece 3, a pole plate 4, a basket assembly 5, a centering spider 6, a radiating cone of felted material, usually paper, 7, a dust cap 8, a voice coil form 9, voice coils 10, for actuating the radiating cone 7, disposed within a voice coil aperature 11, and leads 12 for connecting the voice coils to a source of electrical signals to be reproduced.

As all of the elements enumerated above are well known in the art and form no part of this invention but are referred to here only in the interest of background for a clear understanding of the application of the principles of this invention, a detailed explanation of their various functions is considered unnecessary.

The frequency response of a conventional electro-inechanical speaker of the type illustrated in Figure 2 may be designed to be relatively flat at the low frequency end of the audio spectrum but falls off rapidly as the frequency increases toward the high frequency end of the spectrum. An electrostatic speaker, on the other hand, may be designed to provide a relatively flat response at the high audio frequencies and tends to fall olf rapidly at the lower audio frequencies.

This invention, therefore, proposes to combine the desirable frequency response characteristics of electro-mechanical and electrostatic speakers in a combined high frequency and low frequency radiating medium by superimposing an electrostatic high frequency radiating surface, indicated at 16, Figure 2, upon the low frequency radiating surface of an electro-mechanical device.

To do this, it is suggested that a selected area of the low frequency radiating surface, over which it is desired to superimpose the high frequency radiating surface, be evenly coated by a vacuum condensation process with a metallic substance, such as aluminum. It is preferable that this selected area be physically rough or irregular to permit motion of the high frequency radiating surface, as will be clear later. The metallized area 14 is then covered with a non-hygroscopic, pliable dielectric membrane material 15, such as polyethylene terephthalate sold under the trade name'of Mylar, which, when coated in a manner to be explained later with a conducting film, acts as a high frequency electrostatic diaphragm. This diaphragm should be stretched taut and firmly secured, around its extreme inner and outer peripheral edges .18, to the low frequency radiating surface in a manner to maintain tension and eliminate wrinkling. While the manner in which the diaphragm may be securely held in position is discretionary, examples of the sundry choices available are by gluing or the application of heat and pressure to a thermosensitive substance.

After the high frequency electrostatic diaphragm has been secured in place, its outer or peripheral surface area may also be evenly coated by a vacuum condensation process with a metallic substance, such as aluminum shown at 16.

For a more clear understanding of the mechanical features of this invention, reference is made to Figure 3 which is an exaggerated, fragmentary cross-section view of a portion of Figure 2, as indicated, in which like characters of reference indicate like parts in Figures 2 and 3.

The metallized area 16, of the electrostatic diaphragm, constitutes the high frequency radiating surface. 7 So that the high frequency radiating surface may be energized, light weight conductors 17 are connected to each of the metallized surfaces and brought out, in a conventional manner, for connection to a source of electrical signals to be transduced, thereby providing a means for actuating the high frequency electrostatic diaphragm and radiating ama eur surface. It is apparent that the combination of the two metallized surfaces separated by the dielectric diaphragm material and a small air space, shown at 19, Figure 2, constitutes a capacitor, the metallized surface and the diaphragm being free to vibrate under the influence of electrostatic repulsion. By placing a constantpol'arizing potential across the two metallized surfaces and modulating it with the signals to be transduced, the diaphragm will, therefore, vibrate with the audio signal which will be radiated from the high frequency radiating surface. It is to be specifically understood that the two surfaces which are separated by a dielectric have been referred to as metallized in this specification only for purposes of illustration as these surfaces may be coated with any other conducting material, for example, carbon. Since the theory of operation of electrostatic speakers is Well known in the art, a detailed discussion of these principles is deemed unnecessary-for the purposes of this specification.

Through the application of the principles of this invention, therefore, a combined high frequency and low frequency sound radiating medium is realized, the medium, of course consisting of the combination of a conventional low frequency radiating cone and the/high frequency electrostatic radiating surface superimposed thereon.

In operation, the combined sound radiating medium is vibrated as a unit at the low audio frequencies bya voice coil which is free to move in a magnetic field 'while the,

high frequency radiating surface is independently vibrated at the higher audio frequencies by the electrostatic principle.

The same result, as outlined above, may be realized through the use of a laminated combined high frequency and low frequency sound radiating medium which may be formed by building up alternate layers of non-conducting and conducting materials. In this instance then,--the high frequency radiating diaphragm may be an integral layer or layers of the laminated combined sound-radiating medium thereby dispensing with the requirement of securing this diaphragmto a radiating cone, the radiating surface of which had previously been wholly or partially coated with a conducting material.

Similarly, the high frequency radiating diaphragm'rnay be secured to the selected area of the low frequency radiating cone around its entire area so long as the bonding material used is sufficiently compliant for the purpose. In this instance, of course, the bonding material occupies the space indicated as an air space at 19, Figure 2.

Another possible alternate would be the use of a low frequency radiating cone material which has suflicient compliancy to permit the electrostatic diaphragm to vibrate in one plane and is sufficiently-rigid in -a--transverse plane to permit the unit to vibrate with a piston" action. In this instance, of course, the selected inner and outer surface area of the low frequency radiating cone may be coated with a conducting material.

Inpractical-applications of the principles of this inven tion, design requirements may dictate that the high frequency radiating surface be superimposed upon the enthe peripheral area of the low frequency radiating surface, including or excluding the dust cap. Other-applications may require that only the dust cap areas have'the high frequency radiating surface superimposed thereupon.

It is obvious,therefore, that the principle of this invention may be applied in a variety of applications different from that described herein above.

While I have shown and described a preferred embodiment'of my invention, it will be obvious to-those skilled in the art that various modifications and substitutions may be made from the spirit of this invention which is to be limited'only within the scope of the-appended claims. 'What' is claimed is: 1

1. In a device for converting electrical energytoacoustical energy, a combined high frequency and low frequency sound radiating medium comprising, a low frequency responsive radiating surface, means for actuating said radiating surface, a first conducting layer on a selected area of said radiating surface, an electrostatic diaphragm, a second conducting layer on one side of said electrostatic diaphragm, means for securing the extreme peripheral edges of said electrostatic diaphragm to said selected area of'said radiating surface, an electrostatic diaphragm, a second conducting layer on one side of said electrostatic diaphragm, means for securing the extreme peripheral edges of said electrostatic diaphragm to'said radiating surface in a manner to cover said first conducting layer andto be disposed between said first and second conducting layersand means connected to said conducting layers for actuating said electrostatic diaphragm at a high frequency.

3. In a device for converting electrical energy to acoustical'energy, a combined high frequency and low frequency sound radiating medium comprising, a low frequency responsive radiating cone, means for actuating saiddow frequency radiating cone, a first conducting layer one selected area of the radiating surface of said radiatingcone, an electrostatic diaphragm, a second conducting layer'on one side of said electrostatic diaphragm, means forsecur'ingthe extreme peripheral edges of said electrostatic-diaphragm to the radiating surface of said radiating 7 cone in a'manne'r to cover said first conducting layer and to "be disposed between said first and second conducting layers and means for applying high frequency signals to said first and second conducting layers to thereby-actuate said electrostatic diaphragm.

4.- Ina device for converting electrical energy to acousticalenergy, "a combined high frequency and low frequency sound radiating medium comprising, a low frequency responsive radiating cone, a voice coil for actuating said low frequency radiating cone, a first metallized layer on a selected area of the radiating surface of said radiating cone, an electrostatic diaphragm, a' second metallized layer on one side of saidelect'rostatic diaphragm, means for securing the extreme peripheral edges of said electrostatic diaphragm to the radiating surface of'said radiating cone in a manner to cover said first 'metallized layer and to be disposed between said first and second metalliz'e'd layers and means for connecting high frequency signals across said metallized layers to thereby actuate said electrostatic diaphragm in accordance with said high frequency signals.

5. In a device for converting electrical energy-to acoustical energy, 'a combined high frequency and low frequency sound radiating medium comprising, a low frequency responsive radiating surface, a voice coil for actuating said low frequency radiating surface," a first metal- IiZed' Iayer' on'a selected'area of said radiating surface, an electrostatic diaphragm of non-hygroscopic membrane material, a' second metallized layer onone side-of said electrostatic diaphragm, means for securing the extreme periphefal' edges of said electrostatic diaphragm to said radiating surface in a manner to cover said first metallized layer and to'be disposed between said first and second metallized layers and means for connecting high frequency signals across said metallized layers to thereby actuate saidelectro's tatic diaphragm in accordance with said high frequency signals;

Lem,

quency sound radiating medium comprising, a low frequency responsive radiating cone of a felted material, a voice coil for actuating said low frequency radiating cone in response to low frequency signals applied to said voice coil, a first metallized layer on a selected area of the radiating surface of said radiating cone, an electrostatic diaphragm of non-hygroscopic membrane material, a second metallized layer on one side of said electrostatic diaphragm, means for securing the extreme peripheral edges of said electrostatic diaphragm to the radiating surface of said radiating cone in a manner to cover said first metallized layer and to be disposed between said first and second metallized layers and leads for connecting high frequency signal energy to said first and second metallized layers for actuating said electrostatic diaphragm.

References Cited in the file of this patent UNITED STATES PATENTS Thomas Mar. 22, 1932 Edenburg Aug. 29, 1933 Parry Feb. 11, 1941 Pare July 7, 1942 Marquis Nov. 9, 1948 Howatt Apr. 15, 1952 Brennan May 13, 1952 Lundenberg et a1 Oct. 28, 1952 Olson et a1. Jan. 11, 1955 Whiteley Dec. 31, 1957 FOREIGN PATENTS France June 1, 1955 

